Generally, the faster a CPU runs, the more power the CPU consumes. When a CPU consumes more power, it uses more electricity and generates more heat. With desktop computers, using more power increases energy costs and cooling costs and causes computer manufacturers to spend more money designing and building systems to supply more power and dissipate more heat. This results in computers more expensive to build and operate.
In addition to these energy, design, and construction costs, portable computer users have additional disadvantages associated with CPU power consumption. When operating on battery power, the more power a CPU consumes, the less time the computer can operate without recharging the battery. Buying a bigger, heavier battery adds additional expense and weight to a portable computer. In addition, typically, a bigger battery does not reduce the heat the CPU produces. Reducing power consumption by using a slower CPU, on the other hand, also has disadvantages. A slower CPU reduces the overall performance of the portable computer and makes the portable computer less of a viable replacement for a desktop computer.